1. Field of the Invention
The present invention relates to chalcogen-containing semiconductor materials and, more particularly, to processes for making the same. Specifically, the present invention relates to a novel process for chalcogenizing metal alloys to produce chalcogenide semiconductor materials useful in photovoltaic cells and the like.
2. Description of the Prior Art
The field of photoelectrochemistry and photovoltaics is recognized as having the potential for enabling solar energy utilization to meet many of the energy needs of the future. Through the action of light, photoelectrochemical and photovoltaic cells can be used to generate electric power and/or to synthesize fuels and desired chemicals from abundant, renewable resources. Such photovoltaic cells and their functioning are well documented in the literature. U.S. Pat. No. 4,461,691 provides an excellent background on the general operation of typical photoelectrochemical cells. The contents of this referenced patent are specifically incorporated herein by reference to provide general background information.
Part of the search for efficient, functional photovoltaic cells includes the investigation of various semiconductor materials and processes for making such photosensitive semiconductor materials. One category of materials having important potential use in photovoltaic cells is the chalcogenides. By this is meant any combination of two or more elements, one of which comprises a chalcogen (Group VIa of the Periodic Table-S, Se, Te, and Po).
Prior art devices and fabrication techniques, using polycrystalline semiconductor materials, including chalcogenides, have generally proven inadequate because of high production costs. These high production costs stem from capital equipment costs and high purity control requirements. One such prior art approach includes vacuum evaporation and deposition techniques. Such techniques require extensive vacuum chambers, monitors for each element involved, and relatively high heat. As a result, these techniques tend to be very expensive because of the equipment necessary to operate them.
Another prior approach to producing such semiconductor materials includes spray pyrolysis. In such instances, solutions of each element to be included in the semiconductor material are sprayed onto a hot substrate. Disadvantages to such techniques include poor quality control and nonuniformity. Moreover, such techniques are energy intensive in that they require high temperatures and electric currents.
Still another prior art approach includes electrochemical deposition such as disclosed in U.S. Pat. No. 3,573,177 and British Pat. No. 1,532,616. In such instances, the polycrystalline materials are formed by electrochemical deposition from an electrolyte solution onto an anode surface. Thin films of such materials can be readily formed using these techniques. However, process controls are difficult, and these techniques can be energy intensive. Moreover, the formation of good p-n junctions is difficult using such electrodeposition techniques.